Copolymer, organic solar cell using the same and manufacturing method thereof

ABSTRACT

A copolymer includes a first unit and at least one unit two units different from the first unit. An organic solar cell includes the copolymer in an organic material layer including a photoactive layer.

This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0077495, filed on Aug. 3, 2011, which is hereby incorporated by reference in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a novel copolymer, an organic solar cell comprising the same and a method for fabricating the organic solar cell.

2. Description of the Prior Art

Since the possibility of solar cells based on organic copolymers was first shown by Heeger at the University of California, Santa Barbara (UCSB), in 1992, there have been many studies thereon. Such solar cells include heterojunction thin film devices comprising a mixture of an organic copolymer, which absorbs light, with a C60 or C70 fullerene derivative which has a very high electron affinity. These heterojunction thin film devices comprise a transparent positive electrode made of indium tin oxide (ITO) and a negative electrode made of a metal such as Al, which has a low work function.

The photoactive layer comprising the organic copolymer absorbs light to form electron-hole pairs or excitons. The electron-hole pairs move to the interface between the copolymer and the C60 or C70 fullerene derivative at which they are separated into electrons and holes. Then, the electrons move to the metal electrode, and the holes move to the transparent electrode, thereby generating electrodes.

Currently, the efficiency of organic copolymer thin-film solar cells based on organic copolymers reaches 7-8% (Nature Photonics, 2009, 3, 649-653).

However, the efficiency of the organic copolymer solar cell is still low compared to the maximum efficiency (about 39%) of solar cells based on silicon. Thus, the development of organic polymer solar cells having a higher efficiency is required.

Korean Patent Laid-Open Publication No. 10-2010-0111767 discloses a conductive copolymer comprising 2,7-carbazole in the main chain, and an organic solar cell comprising the same. According to the disclosure of the above patent publication, the conductive copolymer comprising 2,7-carbazole in the main chain improves light absorption and hole mobility to improve the efficiency of the solar cell.

However, there is a problem in that it is not easy to improve optical efficiency, because the mobility of holes is relatively lower than the mobility of electrons, despite the use of 2,7-carbazole.

PRIOR ART DOCUMENTS Patent Documents

-   Korean Patent Laid-Open Publication No. 10-2010-0111767

Non-Patent Documents

-   Macromolecules 2011, 44(7), 1909-1919 -   Nature Photonics, 2009, 3, 649-653 -   B. Nicolas, M. Alexandre, M. Leclerc, Adv. Mater. 19, 2295-2300 -   Y. Human, A. Solyman, I. Ahmed, W. C. Darren, K. James, L. G.     David, J. Mater. Chem. 21, 13649-13656

SUMMARY OF THE INVENTION

It is an object of the present disclosure to provide an organic semiconductor material, which can exhibit excellent electrical properties thanks to its high hole mobility and has high photovoltaic conversion efficiency, and an organic solar cell comprising the same.

To achieve the above object, in one aspect, the present disclosure provides a copolymer comprising a first unit represented by the following formula 1 and at least one unit different from the first unit, wherein the first unit is present in an amount of greater than 0 mole % and 45 mole % or less based on the total moles of monomers constituting the copolymer:

wherein o and p are each an integer ranging from 0 to 3; R_(a) and R_(b) are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R_(a) and R_(b) may form a condensed ring; and R₁ is selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S.

In another aspect, the present disclosure provides a copolymer comprising a first unit represented by the following formula 1, a second unit represented by the following formula 3 and a third unit represented by the following formula 4:

wherein o, p, q and r are each an integer ranging from 0 to 3; s and t are each an integer ranging from 0 to 4; R₁ and R″ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S; R_(a), R_(b) and R₆ to R₁₁ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R_(a), R_(b) and R₆ to R₁₁ may form a condensed ring.

In still another aspect, the present disclosure provides an organic solar cell comprising: a first electrode; a second electrode opposite the first electrode; one or more organic material layers interposed between the first and second electrodes and including a photoactive layer, wherein one or more of the organic material layers comprise the copolymer comprising the first unit of formula 1.

In yet another aspect, the present disclosure provides a method for fabricating an organic solar cell, the method comprising the steps of: preparing a substrate; forming a first electrode on a region of rear sides of the substrate; forming on the first electrode an organic material layer comprising the copolymer including the first unit of formula 1; and forming a second electrode on the organic material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic diagram showing a comparison of charge mobility between 3,6-carbazole-containing copolymers and 2,7-carbazole-containing copolymers.

FIG. 2 is a graphic diagram showing current-voltage curves for organic solar cells of Examples 2 to 4 and Comparative Examples 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present disclosure will be described in detail.

The present disclosure provides a copolymer comprising a first unit represented by formula 1 and at least one unit different from the first unit.

As used herein, the term “unit” means the polymerized form of a repeating monomer unit in the copolymer.

The first unit of formula 1 contains a substituted or unsubstituted 3,6-carbazole group. An organic solar cell comprising the copolymer including the first unit has high charge mobility compared to an organic solar cell comprising a 2,7-carbazole-containing copolymer, and the first unit of formula 1 contributes to the stability of the copolymer.

FIG. 1 is a graphic diagram showing a comparison of charge mobility between 3,6-carbazole-containing copolymers and 2,7-carbazole-containing copolymers.

In one embodiment of the present disclosure, the first unit of formula 1 is preferably present in an amount of greater than 0 mole % and 45 mole % or less based on the total moles of monomers constituting the copolymer.

In another embodiment, the content of the first unit of formula 1 is 0.1-30 mole % based on the total moles of the monomers. In still another embodiment, the content of the first unit of formula 1 is 0.5-20 mole % based on the total moles of the monomers. In yet another embodiment, the content of the first unit of formula 1 is 0.5-15 mole % based on the total moles of the monomers. In another further embodiment, the content of the first unit of formula 1 is 1-10 mole % based on the total moles of the monomers.

In the 3,6-carbazole-containing copolymer, a nitrogen atom is conjugated to the main chain to stabilize holes and increase the mobilities of holes and electrons, so that, hole mobility and electron mobility in the organic solar cell comprising the copolymer can be balanced. Thus, the present disclosure provides an organic semiconductor material, which can exhibit excellent electrical properties thanks to the balance between hole mobility and electron mobility and has high photovoltaic conversion efficiency, and an organic solar cell comprising the same.

Conventional 2,7-carbazole-containing copolymers do not appear to exhibit excellent electrical properties, because no nitrogen atom is not conjugated to the main chain.

In contrast, if the content of the first unit of formula 1 in the copolymer comprising the first unit of formula 1 is 45 mole % or less based on the total moles of monomers constituting the copolymer, a reduction in the optical absorption of the copolymer, which results from the relatively low absorbance of the carbazole group, can be minimized. In addition, in this case, a copolymer having a suitable molecular weight can be prepared.

In one embodiment of the present disclosure, the unit different from the first unit in the copolymer includes at least one electron acceptor.

In one embodiment of the present disclosure, the electron acceptor is present in an amount of greater than 0 mole % and 50 mole % or less based on the total moles of monomers constituting the copolymer.

In another embodiment of the present disclosure, the unit different from the first unit in the copolymer includes at least one electron acceptor and at least one electron donor.

In still another embodiment of the present disclosure, the unit different from the first unit in the copolymer includes at least two electron acceptors and at least one electron donor.

Examples of the substituents of the above formulas will be described below, but are not limited thereto.

In the present disclosure, the alkyl group may be a straight or branched-chain alkyl group, and the number of carbon atoms thereof is preferably 1 to 20, but is not limited thereto. Specific examples of the alkyl group include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, t-butyl, pentyl, hexyl and heptyl groups.

In the present disclosure, the alkenyl group may be a straight or branched-chain alkenyl group, and the number of carbon atoms thereof is preferably 2 to 40, but is not limited thereto. Specific examples of the alkenyl group include, but are not limited to, aryl-substituted alkenyl groups, such as stylbenzyl and styrenyl groups.

In the present disclosure, the alkoxy group may be a straight, branched or cyclic chain alkoxy group. The number of carbon atoms of the alkoxy group is preferably 1 to 25, but is not limited thereto. Specific examples of the alkoxy group include, but are not limited to, methoxy, ethoxy, n-propyloxy, iso-propyloxy, n-butyloxy and cyclopentyloxy groups.

In the present disclosure, the cycloalkyl group preferably contains 3 to 60 carbon atoms, but is not limited thereto. Particularly preferred examples of the cycloalkyl group include cyclopentyl and cyclohexyl groups.

In the present disclosure, the halogen group may be fluorine, chlorine, bromine or iodine.

In the present disclosure, the aryl group may be monocyclic, and the number of carbon atoms thereof is preferably 6 to 60, but is not limited thereto. Specific examples of the aryl group include, but are not limited to, monocyclic aromatic groups, such as phenyl, biphenyl, triphenyl, terphenyl or stilbene groups, and polycyclic aromatic groups, such as naphthyl, anthracenyl, phenanthrenyl, pyrenyl, perylenyl, tetracenyl, chrysenyl, fluorenyl, acenaphthacenyl, triphenylene or fluoranthene groups.

In the present disclosure, the heterocyclic group is a heterocyclic group containing at least one heteroatom selected from among O, N and S, and the number of carbon atoms thereof is preferably 2 to 60, but is not limited thereto. Examples of the heterocyclic group include, but are not limited to, thiophene, furan, pyrrol, imidazole, thiazole, oxazole, oxadiazole, triazole, pyridyl, bipyridyl, triazine, acridyl, pyridazine, quinolinyl, isoquinolinyl, indole, carbazole, benzoxazole, benzothiazole, benzimidazole, benzocarbazole, benzothiophene, dibenzothiophene, benzofuranyl, phenanthroline and dibenzofuranyl groups.

In the present disclosure, the imide group preferably contains 1 to 25 carbon atoms, but is not limited thereto. Specific examples of the imide group include, but are not limited to, compounds having the following formulas:

In the present disclosure, the amide group is an amide group whose nitrogen may be mono- or di-substituted with hydrogen, a straight, branched or cyclic chain alkyl group containing 1 to 25 carbon atoms or an aryl group containing 6 to 25 carbon atoms. Specific examples of the amide group include, but are not limited to, compounds having the following formulas:

In the present disclosure, the ester group is an ester group whose oxygen may be substituted with a straight, branched or cyclic chain alkyl group containing 1 to 25 carbon atoms or an aryl group containing 6 to 25 carbon atoms. Specific examples of the ester group include, but are not limited to, compounds having the following formulas:

In the present disclosure, the heteroaryl group may be selected from among the above-described examples of the heterocyclic group.

In the present disclosure, the fluorenyl group has a structure in which two cyclic organic compounds are linked to each other by one atom, and examples thereof include

and the like.

In the present disclosure, the fluorenyl groups include an open fluorenyl group having a structure in which one of two cyclic compounds linked to each other by one atom is broken. Examples of the open fluorenyl group include

and the like.

In the present disclosure, the amine group preferably contains 1 to 30 carbon atoms, but is not limited thereto. Specific examples of the amine group include, but are not limited to, methylamine, dimethylamine, ethylamine, diethylamine, phenylamine, naphthylamine, biphenylamine, anthracenylamine, 9-methyl-anthracenylamine, diphenylamine, phenylnaphthylamine, ditolylamine, phenyltolylamine and triphenylamine groups.

In the present disclosure, examples of the arylamine group include substituted or unsubstituted monocyclic diarylamine, substituted or unsubstituted polycyclic diarylamine, and substituted or unsubstituted monocyclic or polycyclic diarylamine groups.

In the present disclosure, the aryl group of the aryloxy, arylthioxy, arylsulfoxy and aralkylamine groups is as defined above for the aryl group.

In the present disclosure, the alkyl group of the alkylthioxy, alkylsulfoxy, alkylamine and aralkylamine groups is as defined above for the alkyl group.

In the present disclosure, the heteroaryl group of the heteroarylamine group may be selected from among the above-described examples of the heterocyclic group.

In the present disclosure, the arylene, alkenylene, fluorenylene, carbazolylene and heteroarylene groups are divalent aryl, alkenyl, fluorenyl and carbazole groups, respectively. These groups are as defined above for the aryl, alkenyl, fluorenyl and carbazole groups, except that they are divalent groups.

As used herein, the term “substituted or unsubstituted” means that it is unsubstituted or substituted with one or more selected from the group consisting of deuterium, a halogen group, an alkyl group, an alkenyl group, an alkoxy group, a cycloalkyl group, a silyl group, an arylalkenyl group, an aryl group, an aryloxy group, an alkylthioxy group, an alkylsulfoxy group, an arylsulfoxy group, a boron group, an alkylamine group, an aralkylamine group, an arylamine group, a heteroaryl group, a carbazole group, an arylamine group, an aryl group, a fluorenyl group, a nitrile group, a nitro group, a hydroxyl group, and a heterocyclic group containing at least one heteroatom selected from among N, O and S.

In the present disclosure, the electron acceptor and the electron donor may be any conventional electron acceptor and electron donor known in the field of organic solar cells. Specifically, the electron acceptor is a carbon-based aromatic compound or a heteroaromatic compound containing at least one heteroatom selected from among sulfur, phosphorus, nitrogen, selenium and the like.

In one embodiment of the present disclosure, the unit different from the first unit in the copolymer includes at least one of electron acceptors represented by the following formulas:

wherein R₂ to R₅ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₂ to R₅ may form a condensed ring; X₁ and X₂ are the same or different and are each independently selected from the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se and Te; and Y₁ to Y₄ are the same or different and are each independently selected from the group consisting of CR, N, SiR, P and GeR, wherein R and R′ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R and R′ may form a condensed ring.

In another embodiment of the present disclosure, the unit different from the first unit in the copolymer includes at least one of the electron donors represented by the following formulas:

wherein a is an integer ranging from 0 to 4; b is an integer ranging from 0 to 6; c is an integer ranging from 0 to 8; d and e are each an integer ranging from 0 to 3; R₂ and R₃ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₂ and R₃ may form a condensed ring; X₁ to X₃ are the same or different and are each independently selected from the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se and Te; Y₁ and Y₂ are the same or different and are each independently selected from the group consisting of CR, N, SiR, P and GeR; wherein R and R′ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R and R′ may form a condensed ring.

In one embodiment of the present disclosure, the copolymer comprises one represented by the following formula 2:

wherein l is a mole fraction in the range of 0<1≦l; m is a mole fraction in the range of 0≦m<1; l+m=1; n is an integer ranging from 1 to 10,000; A is represented by formula 1; B, C and D are the same or different and are each independently an electron acceptor or an electron donor; and at least one of B, C and D is an electron acceptor.

In one embodiment of the present disclosure, B in formula 2 is an electron acceptor.

In another embodiment, D in formula 2 is an electron acceptor.

In still another embodiment, B and D in formula 4 are each an electron acceptor.

In one embodiment of the present disclosure, the electron acceptor in the copolymer is represented by the following formula 3:

wherein s and t are each an integer ranging from 0 to 4; and R₈ to R₁₁ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₈ to R₁₁ may form a condensed ring.

In another embodiment of the present disclosure, the electron donor in the copolymer is represented by the following formula 4:

wherein q and r are each an integer ranging from 0 to 3; R₆ and R₇ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₆ and R₇ may form a condensed ring; and R″ is selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted M or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S.

The copolymer of the present disclosure comprises a 2,7-carbazole unit in addition to a 3,6-carbazole unit. This 2,7-carbazole unit provides low band gap energy and is highly stable against chemical and thermal attacks, air and moisture compared to other electron donors, so that it improves the efficiency of the organic solar cell comprising the copolymer.

In one embodiment of the disclosure, the unit of formula 4 in the copolymer is present in an amount of more than 0 mole % and 40 mole % or less based on the total moles of monomers constituting the copolymer.

In another embodiment, the present disclosure provides a copolymer comprising the first unit of formula 1, the second unit of formula 3 and the third unit of formula 4.

In still another embodiment, the present disclosure provides a copolymer comprising the first unit of formula 1, the second unit of formula 3 and the third unit of formula 4, wherein the first unit of formula 1 is present in an amount of greater than 0 mole % and 10 mole % or less based on the total moles of monomers constituting the copolymer, the second unit of formula 3 is present in an amount of greater than 0 mole % and 50 mole % or less based on the total moles of the monomers, and the third unit of formula 4 is present in an amount of more than 0 mole % and 40 mole % or less based on the total moles of the monomers.

In still another embodiment, unit C of formula 2 is the electron acceptor of formula 3.

In still another embodiment, unit B of formula 2 is the electron donor of formula 4.

In still another embodiment, unit D of formula 2 is the electron donor of formula 4.

In still another embodiment, units B and C of formula 2 are each represented by formula 4.

In one embodiment of the present disclosure, the copolymer is represented by the following formula 5:

wherein R₁, R_(a), R_(b), o and p are as defined in formula 1; q and r are each an integer ranging from 0 to 3; s and t are each an integer ranging from 0 to 4; l is a mole fraction in the range of 0<l≦1; m is a mole fraction in the range of 0≦m<1; l+m=1; n is an integer ranging from 1 to 10,000; R″ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S; and R₆ to R₁₁ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S; or adjacent two of R₆ to R₁₁ may form a condensed ring.

In one embodiment of the present disclosure, R_(a) is hydrogen.

In another embodiment of the present disclosure, R_(b) is hydrogen.

In another embodiment of the present disclosure, s and t are each 1.

In still another embodiment of the present disclosure, R₈ is hydrogen.

In still another embodiment of the present disclosure, R₉ is hydrogen.

In still another embodiment of the present disclosure, is hydrogen.

In still another embodiment of the present disclosure, is hydrogen.

In still another embodiment of the present disclosure, is hydrogen.

In yet another embodiment of the present disclosure, R is hydrogen.

In one embodiment of the present invention, the copolymer further comprises a fourth unit represented by the following formula 6 and a fifth unit represented by the following formula 7:

wherein l is a mole fraction in the range of 0<l≦1; m is a mole fraction in the range of 0≦m<1; l+m=1; R₁ is as defined in formula 1 above; and R″ is as defined in formula 4 above.

In one embodiment of the present disclosure, the end group of the copolymer is selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S.

In one embodiment of the present disclosure, the end group of the copolymer is a heterocyclic group.

In another embodiment of the present disclosure, the end group of the copolymer is an aryl group.

In one embodiment of the present disclosure, the copolymer preferably has a number-average molecular weight of 500-1,000,000 g/mol, and more preferably 10,000-100,000 g/mol.

In one embodiment of the present disclosure, the copolymer may have a molecular weight distribution of 1-100. Preferably, the copolymer has a molecular weight distribution of 1-3.

As the molecular weight distribution decreases and the number-average molecular weight increases, the electrical and mechanical properties of the copolymer improve.

In addition, in order for the copolymer to have a specific level or higher of solubility so that a solution application method is advantageously applied, the copolymer preferably has a number-average molecular weight of 100,000 or less.

The copolymer comprising the unit of formula 1 can be prepared based on Preparation Examples as described below.

The copolymer according to the present disclosure can be prepared by a multi-step chemical reaction. Specifically, monomers can be prepared by an alkylation reaction, the Grignard reaction, the Suzuki coupling reaction and the Stille coupling reaction, after final polymers can be prepared from the monomers by a carbon-carbon coupling reaction such as the Stille coupling reaction. When the substituent to be introduced is a boronic acid or boronic ester compound, the copolymer can be prepared by the Suzuki coupling reaction, and when the substituent to be introduced is a tributyltin compound, the copolymer can be prepared by the Stille coupling reaction, but is not limited thereto.

In another aspect, the present disclosure provides an organic solar cell comprising the copolymer containing the unit of formula 1.

Specifically, the present disclosure provides an organic solar cell comprising: a first electrode; a second electrode opposite the first electrode; and one or more organic material layers interposed between the first electrode and the second electrode and including a photoactive layer, wherein one or more of the organic material layers comprise the above-described copolymer.

In one embodiment of the present disclosure, the organic solar cell comprises the first electrode, the photoactive layer and the second electrode. The organic solar cell may further comprise a substrate, a hole transport layer and/or an electron transport layer.

The substrate may be a glass or transparent substrate having excellent transparency, surface smoothness, ease of handling, and water resistance, but is not limited thereto.

The substrate is not limited as long as it is commonly used in organic solar cells. Specific examples of the substrate include, but are not limited to, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene (PP), polyimide (PI) and triacetyl cellulose (TAC).

The first electrode may be made of a transparent, highly conductive material, but is not limited thereto. Specific examples of the material of the first electrode include, but are not limited to, indium tin oxide (ITO), tin oxide (SnO₂) and zinc oxide (ZnO).

The second electrode may be made of a metal having a low work function, but is not limited thereto. Specific examples of the material of the second electrode include, but are not limited to, metals, such as lithium, magnesium or aluminum, alloys thereof, and multilayer materials, such as Al:Li, Al:BaF₂, or Al:BaF₂:Ba.

The hole transport layer and/or the electron transport layer may be made of a material which efficiently transfers electrons and holes to the photoactive layer to increase the mobility of produced charges to the electrodes, but is not limited thereto.

Examples of the material of the hole transport layer induce PEDOT:PSS (poly(3,4-ethylenediocythiophene) doped with poly(styrenesulfonic acid)), and N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (TPD). Examples of the material of the electron transport layer include aluminum trihydroxyquinoline (Alq₃), the 1,3,4-oxadiazole derivative PBD (2-(4-biphenyl)-5-phenyl-1,3,4-oxadiazole), the quinoxaline derivative TPQ (1,3,4-tris[(3-phenyl-6-trifluoromethyl)quinoxaline-2-yl]benzene), and triazole derivatives.

The photoactive layer may comprise an electron donor material and an electron acceptor material.

In one embodiment of the present disclosure, the electron donor material is the copolymer comprising the first unit of formula 1.

In one embodiment of the present disclosure, the electron acceptor material may be selected from the group consisting of fullerene, fullerene derivatives, vasocuproin, semiconductor elements, semiconductor compounds, or combinations thereof. Specifically, the electron acceptor material may be phenyl C₆₁-butyric acid methyl ester (PC₆₁BM) or phenyl C₇₁-butyric acid methyl ester (PC₇₁BM).

The electron donor material and the electron acceptor material in the photoactive layer can form a bulk heterojunction (BHJ). The electron donor material and the electron acceptor material may be mixed with each other at a ratio of 1:10-10:1 (w/w). After the electron donor material and the electron acceptor material have been mixed, they may be annealed at a temperature of 30 to 300° C. for 1 second to 24 hours in order to maximize the characteristics thereof.

The thickness of the photoactive layer may be 10-10,000 Å, but is not limited thereto.

In one embodiment of the present disclosure, a buffer layer may further be introduced between the photoactive layer and the first electrode, and an electron transfer layer, a hole blocking layer or an optical space layer may further be introduced between the photoactive layer and the second electrode.

As described in Korean Patent Laid-Open Publication No. 10-2010-0111767 which is incorporated herein by reference, in one preferred embodiment, the organic solar cell comprises the substrate, the first electrode, the photoactive layer and the second electrode. Herein, the photoactive layer comprises an electrode donor made of the copolymer, which comprises the first unit of formula 1, and an electron acceptor made of a C60 fullerene derivative or a C70 fullerene derivative.

In one embodiment of the present disclosure, the photovoltaic material of the photoactive layer comprises the copolymer comprising the first unit of formula 1, and the electron acceptor, which are mixed with each other at a weight ratio of 1:0.5-1:4.

In another embodiment of the present disclosure, the photovoltaic material of the photoactive layer comprises the copolymer comprising the first unit of formula 1, and a C60 fullerene derivative or a C70 fullerene derivative, which are mixed with each other at a weight ratio of 1:0.5-1:4.

If the fullerene derivative is used at a weight ratio of less than 0.5 relative to the copolymer comprising the first unit of formula 1, the mobility of electrons will be insufficient, because the content of the crystallized fullerene derivative will be insufficient, and if the fullerene derivative is used at a weight ratio of more than 4, the efficient absorption of light into the photoactive layer will not be achieved, because the amount of the copolymer comprising the first unit of formula 1 is relatively reduced.

In one embodiment of the present disclosure, the organic solar cell may either comprise an anode, a photoactive electrode and a cathode, which are arranged in that order, or comprise a cathode, a photoactive layer and an anode, which are arranged in that order, but the scope of the present invention is not limited thereto.

In another embodiment of the present disclosure, the organic solar cell may either comprise an anode, a hole transport layer, a photoactive layer, an electron transport layer and a cathode, which are arranged in that order, or comprise a cathode, an electron transport layer, a photoactive layer, a hole transport layer and an anode, which are arranged in that order, but the scope of the present invention is not limited thereto.

The organic solar cell of the present disclosure can be fabricated using the same materials and method as known in the art, except that the organic material layers comprise the copolymer comprising the first unit of formula which is the compound of the present disclosure.

In another aspect, the present disclosure provides a method for fabricating an organic solar cell, the method comprising the steps of: preparing a substrate; forming a first electrode on a region of rear sides of the substrate; forming on the first layer an organic material layer comprising the copolymer including the first unit of formula 1; and forming a second electrode on the organic material layer.

The organic solar cell of the present invention can be fabricated, for example, by sequentially depositing the first electrode, the organic material layer and the second electrode on the substrate. Herein, the deposition can be performed using wet coating methods, including gravure printing, offset printing, screen printing, inkjet printing, spin coating, and spray coating, but is not limited thereto.

In the organic solar cell comprising the copolymer including the first unit of formula 1, the copolymer can serve as an electron donor.

Hereinafter, a method for preparing the first unit of formula 1, and a method for fabricating an organic solar cell using these units will be described in detail with reference to examples. It is to be understood, however, that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1 Synthesis of Monomers Example 1-A Preparation of N-9′-heptadecanyl-3,6-dibromocarbazole

In this Example, 9-heptadecane p-toluenesulfonate was prepared with reference to the literature (B. Nicolas, M. Alexandre, M. Leclerc, Adv. Mater. 19, 2295-2300).

3,6-Dibromo-9H-carbazole (4.00 g, 12.3 mmol) and potassium hydroxide (6.90 q, 123 mmol) were added to 30 ml of anhydrous dimethyl sulfoxide and stirred for 1 hour. Then, 9-heptadecane p-toluenesulfonate (7.58 g, 18.5 mmol) was added thereto and stirred for 12 hours.

The mixture was cooled to room temperature, extracted with hexane/ethyl acetate (3:1 v/v) and washed with water, after which the solution was dried with magnesium sulfate (MgSO₄) to remove water. The solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography to afford a white solid.

Yield: 86%

¹H NMR: (300 MHz, CDCl3, ppm): δ 8.16 (br, 2H); 7.48 (br, 4H); 4.47 (br, 1H); 2.23 (br, 2H); 1.90 (br, 2H); 1.11 (br, 24H); 0.83 (t, J=7.1 Hz, 6H)

¹³C NMR (75 MHz, CDCl₃, ppm): δ 129.39; 128.93; 123.73; 123.40; 113.42; 110.94; 57.23; 34.03; 32.13; 29.68; 29.66; 29.50; 27.02; 22.99; 14.47

m.p.: 53.6 to 55.7° C.

HRMS (EI⁺, m/z) [M]⁺ calculated for C₂₉H₄₁Br₂N: 561.1606. found: 561.1608.

Example 1-B Preparation of 3,6-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole

N-9′-Heptadecanyl-3,6-dibromocarbazole (4.00 q, 7.10 mmol) was added to and dissolved in 30 ml of anhydrous tetrahydrofuran) and cooled to −78° C., and 1.7 M n-butyllithium in hexane (17.5 ml, 29.8 mmol) was added thereto. The mixture was stirred for 1 hour, and then 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (5.28 g, 28.4 mmol) was added at a time thereto. Then, the mixture was warmed to room temperature and stirred for 12 hours.

Water was added to the mixture to stop the reaction, and the mixture was extracted with diethyl ether and washed with water, after which the solution was dried with magnesium sulfate (MgSO₄) to remove water. The solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography to afford a white solid.

Yield: 57%

¹H NMR (300 MHz, CDCl₃, ppm): δ 8.68 (br, 2H); 7.87 (br, 2H); 7.56 (br, 1H); 7.39 (br, 1H); 4.58 (br, 1H); 2.29 (br, 2H); 1.90 (br, 2H); 1.39 (br, 24H); 1.13 (br, 24H); 0.81 (t, J=6.8 Hz, 6H)

¹³C NMR (75 MHz, CDCl₃, ppm): δ 144.61; 141.20; 132.08; 128.40; 124.25; 122.85; 111.39; 108.66; 83.90; 56.94; 34.10; 32.14; 29.68; 27.10; 25.36; 22.99; 14.47

m.p.: 147.8˜149.2° C.

HRMS (EI⁺, m/z) [M]⁺ calculated for C₂₉H₄₁Br₂N: 567.5100. found: 567.5103

In this Example, 2,7-bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole was prepared with reference to the literature (B. Nicolas, M. Alexandre, M. Leclerc, Adv. Mater. 19, 2295-2300).

Example 2 Synthesis of Copolymer 1

3,6-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole (4.1 mg, 0.006 mmol), 2,7-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole (201 mg, 0.306 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammonium hydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat 336 were added to 3 ml of toluene and stirred under reflux. After 72 hours, phenylboronic acid (0.05 g) was added to and reacted with the reaction mixture for 3 hours, after which bromobenzene (0.12 g) was added to and reacted with the mixture for 4 hours. Then, the mixture was cooled to room temperature and poured into methanol. The solid was filtered and Soxhlet-extracted with acetone, hexane and chloroform. The extract was precipitated in methanol, and the solid was filtered.

Yield: 55%

Number-average molecular weight: 9,400 g/mol

Weight-average molecular weight: 33,300 g/mol

Example 3 Synthesis of Copolymer 2

3,6-Bis(4′,4′,5′5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole (20.5 mg, 0.030 mmol), 2,7-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole (184 mg, 0.281 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammonium hydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat 336 were added to 3 ml of toluene and stirred under reflux. After 72 hours, phenylboronic acid (0.05 g) was added to and reacted with the reaction mixture for 3 hours, after which bromobenzene (0.12 g) was added to and reacted with the mixture for 4 hours. Then, the mixture was cooled to room temperature and poured into methanol. The solid was filtered and Soxhlet-extracted with acetone, hexane and chloroform. The extract was precipitated in methanol, and the solid was filtered.

Yield: 58%

Number-average molecular weight: 11,100 g/mol

Weight-average molecular weight: 56,400 g/mol

Example 4 Synthesis of Copolymer 3

3,6-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2,7-yl)—N-9′-heptadecanylcarbazole (41.0 mg, 0.062 mmol), 2,7-heptadecanylcarbazole (164 mg, 0.250 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammonium hydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat 336 were added to 3 ml of toluene and stirred under reflux. After 72 hours, phenylboronic acid (0.05 g) was added to and reacted with the reaction mixture for 3 hours, after which bromobenzene (0.12 g) was added to and reacted with the mixture for 4 hours. Then, the mixture was cooled to room temperature and poured into methanol. The solid was filtered and Soxhlet-extracted with acetone, hexane and chloroform extract was precipitated in methanol, and the solid was filtered.

Yield: 60%

Number-average molecular weight: 10,700 g/mol

Weight-average molecular weight: 20,500 g/mol

Comparative Example 1 Synthesis of Copolymer 4

2,7-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)—N-9′-heptadecanylcarbazole (205 mg, 0.312 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (143 mg, 0.312 mmol), a 20% aqueous solution of tetraethylammonium hydroxide, tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat 336 were added to 3 ml of toluene and stirred under reflux. After 72 hours, phenylboronic acid (0.05 g) was added to and reacted with the reaction mixture for 3 hours, after which bromobenzene (0.12 g) was added to and reacted with the mixture for 4 hours. Then, the mixture was cooled to room temperature and poured into methanol. The solid was filtered and Soxhlet-extracted with acetone, hexane and chloroform. The extract was precipitated in methanol, and the solid was filtered.

Comparative Example 2 Synthesis of Copolymer 5

3,6-Bis(4′,4′,5′,5′-tetramethyl-1′,3′,2′-dioxaborolan-2′-yl)-N-9′-heptadecanylcarbazole (200 mg, 0.304 mmol), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (139 mg, 0.304 mmol), a 20% aqueous solution of tetraethylammonium hydroxide (3 ml), tetrakis(triphenylphosphine)palladium (0) (5 mg) and Aliquat 336 were added to 3 ml of toluene and stirred under reflux. After 72 hours, phenylboronic acid (0.05 g) was added to and reacted with the reaction mixture for 3 hours, after which bromobenzene (0.12 g) was added to and reacted with the mixture for 4 hours. Then, the mixture was cooled to room temperature and poured into methanol. The solid was filtered and Soxhlet-extracted with acetone, hexane and chloroform. The extract was precipitated in methanol, and the solid was filtered.

Yield: 42%

Number-average molecular weight: 4,500 g/mol

Weight-average molecular weight: 6,100 g/mol

Fabricate of Organic Solar Cells and Measurement of Properties Thereof

Each of the above-prepared copolymers and PC₇₁BM (|6,6|-phenyl C₆₁ butyric acid methyl ester were dissolved in 1,2-dichlorobenzene (DCB) to prepare composite solutions. Herein, the concentration of the copolymer in the composite solution was adjusted to 1-2 wt %. In order to fabricate organic solar cells having a structure of ITO/PEDOT:PSS/photoactive layer/LiF/Al, a glass substrate coated with ITO was ultrasonically washed with distilled water, acetone and 2-propanol, and the surface of the ITO was treated with ozone for 10 minutes, and then spin-coated with PEDOT:PSS (AI 4083) to a thickness of 25 nm, followed by heat treatment at 235° C. for 10 minutes. For coating of the photoactive layer, each of the polymer-PC₇₁BM composite solutions was filtered with a 0.45-μm PP syringe filter and spin-coated on the PEDOT:PSS layer, followed by heat treatment at 120° C. for 5 minutes. Then, LiF was deposited on the photoactive layer to a thickness of 6 Å under a vacuum of 3×10⁻⁸ torr using a thermal evaporator, after which Al was deposited on the LiF to a thickness of 120 nm. The photovoltaic properties of the organic solar cells fabricated as described above were measured under a condition of 100 mW/cm² (AM 1.5), and the results of the measurement are shown in Table 1 below.

TABLE 1 Properties of organic solar cells short circuit open circuit power conversion Molar ratio (%) current density voltage Fill efficiency Copolymer of 3,6-carbazole (mA/cm2) (V) factor (%) Example 2 Copolymer 1 1 13.6 0.91 50 6.2 Example 3 Copolymer 2 5 10.5 0.91 50.9 4.9 Example 4 Copolymer 3 10 10.9 0.92 41.3 4.2 Comparative Copolymer 4 0 12.6 0.91 39.6 4.6 Example 1 Comparative Copolymer 5 100 1.8 0.50 23.6 0.2 Example 2

FIG. 2 is a graphic diagram showing current-voltage curves for the organic solar cells.

As can be seen from the results in Table 1 above, the organic solar cells of Examples 2 to 4, which comprise the copolymer including the first unit of formula 1, had increased efficiency compared to the organic solar cell of Comparative Example 1, comprising the copolymer which does not include the first unit of formula 1, and the organic solar cell of Comparative Example 2, which comprises the copolymer including only the first unit of formula 1.

As can be seen from the results in Table 1, the short-circuit density, fill factor and energy conversion efficiency of the organic solar cells were influenced by the molar ratio of the first unit of formula 1.

Accordingly, it can be concluded that the mobility of holes in the photoactive layer of the organic solar cell is increased due to the presence of 3,6-carbazole so as to approach the mobility of electrons, thereby increasing the energy conversion efficiency of the organic solar cell.

As described above, the copolymer of the present disclosure can be used as a material for the organic material layer of an organic solar cell, and an organic solar cell comprising the same can exhibit excellent properties, including increased open voltage and increased efficiency. In particular, the novel copolymer according to the present disclosure has a deep HOMO level and high charge mobility, and thus can exhibit excellent properties. Furthermore, the copolymer according to the present invention may be used in a pure or impure form in an organic solar cell and may be applied using a solution application method. In addition, the copolymer of the present disclosure can increase the optical efficiency of the organic solar cell and improve the cycle life characteristics of the organic solar cell thanks to its thermal stability. 

What is claimed is:
 1. A copolymer comprising a first unit represented by the following formula 1 and at least two units different from the first unit, wherein the two units different from the first unit include at least one electron acceptor and at least one electron donor, the electron donor is represented by the following formula 4, and the first unit is present in an amount of 1 mole % to 5 mole % based on the total moles of monomers constituting the copolymer:

wherein o and p are each an integer ranging from 0 to 3; R_(a) and R_(b) are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R_(a) and R_(b) may form a condensed ring; and R₁ is selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S;

wherein q and r are each an integer ranging from 0 to 3; R₆ and R₇ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₆ and R₇ may form a condensed ring; and R″ is selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S.
 2. The copolymer of claim 1, wherein the electron acceptor is present in an amount of 1 mole % to 5 mole % based on the total moles of the monomers.
 3. The copolymer of claim 1, wherein the unit different from the first unit includes at least two electron acceptors and at least one electron donor.
 4. The copolymer of claim 1, wherein the unit different from the first unit includes at least one of electron acceptors represented by the following formulas:

wherein R₂ to R₅ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₂ to R₅ may form a condensed ring; X₁ to X₃ are the same or different and are each independently selected from the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se and Te; and Y₁ to Y₄ are the same or different and are each independently selected from the group consisting of CR, N, SiR, P and GeR; wherein R and R′ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R and R′ may form a condensed ring.
 5. The copolymer of claim 1, wherein the unit different from the first unit includes at least one of electron donors represented by the following formulas:

wherein a is an integer ranging from 0 to 4; b is an integer ranging from 0 to 6; c is an integer ranging from 0 to 8; d and e are each an integer ranging from 0 to 3; R₂ and R₃ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₂ and R₃ may form a condensed ring; X₁ to X₃ are the same or different and are each independently selected from the group consisting of CRR′, NR, O, SiRR′, PR, S, GeRR′, Se and Te; and Y₁ and Y₂ are the same or different and are each independently selected from the group consisting of CR, N, SiR, P and GeR, wherein R and R′ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S.
 6. The copolymer of claim 1, wherein the copolymer comprises one represented by the following formula 2:

wherein l is a mole fraction in the range of 0<l≦1; m is a mole fraction in the range of 0≦m<1; l+m=1; n is an integer ranging from 1 to 10,000; A is represented by formula 1; B, C and D are the same or different and are each independently an electron acceptor or an electron donor; at least one of B, C, and D is represented by formula 4; and at least one of B, C and D is an electron acceptor.
 7. The copolymer of claim 1, wherein the electron acceptor is represented by the following formula 3:

wherein and t are each an integer ranging from 0 to 4; R₈ to R₁₁ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₈ to R₁₁ may form a condensed ring.
 8. A copolymer comprising a first unit represented by the following formula 1, a second unit represented by the following formula 3 and a third unit represented by the following formula 4:

wherein o, p, q and r are each an integer ranging from 0 to 3; S and t are each an integer ranging from 0 to 4; R₁ and R″ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S; R_(a), R_(b) and R₆ to R₇ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R_(a), R_(b) and R₆ to R₇ may form a condensed ring; and R₈ to R₁₁ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₈ to R₁₁ may form a condensed ring.
 9. The copolymer of claim 8, wherein the first unit is present in an amount of 1 mole % to 5 mole % based on the total moles of monomers constituting the polymer, the second unit is present in an amount of greater than 0 mole % and 50 mole % or less based on the total moles of the monomers, and the third unit is present in an amount of more than 0 mole % and 40 mole % or less based on the total moles of the monomers.
 10. The copolymer of claim 1, wherein the copolymer is represented by the following formula 5:

wherein R₁, R_(a), R_(b), o and p are as defined in formula 1; q and r are each an integer ranging from 0 to 3; s and t are each an integer ranging from 0 to 4; l is a mole fraction in the range of 0<l<1; m is a mole fraction in the range of 0≦m<1; l+m=1; n is an integer ranging from 1 to 10,000; R″ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S; and R₆ to R₇ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₇ may form a condensed ring; and R₈ to R₁₁ are the same or different and are each independently selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S, or adjacent two of R₈ to R₁₁ may form a condensed ring.
 11. The copolymer of claim 1, wherein the copolymer further comprises a fourth unit represented by the following formula 6 and a fifth unit represented by the following formula 7:

wherein R₁ is as defined in formula 1; l is a mole fraction in the range of 0<l≦1; m is a mole fraction in the range of 0≦m<1; l+m=1; and R″ is selected from the group consisting of hydrogen, deuterium, a halogen group, a nitrile group, a nitro group, an imide group, an amide group, a hydroxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkylthioxy group, a substituted or unsubstituted arylthioxy group, a substituted or unsubstituted alkylsulfoxy group, a substituted or unsubstituted arylsulfoxy group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted boron group, a substituted or unsubstituted alkylamine group, a substituted or unsubstituted aralkylamine group, a substituted or unsubstituted arylamine group, a substituted or unsubstituted heteroarylamine group, a substituted or unsubstituted aryl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted carbazole group, and a substituted or unsubstituted heterocyclic group containing at least one heteroatom selected from among N, O and S.
 12. The copolymer of claim 1, wherein the copolymer has an aryl group as its end group.
 13. The copolymer of claim 1, wherein the copolymer has a heterocyclic group as its end group.
 14. The copolymer of claim 1, wherein the copolymer has a number-average molecular weight of 500-1,000,000 g/mol.
 15. The copolymer of claim 1, wherein the copolymer has a molecular weight distribution of 1-100.
 16. An organic solar cell comprising: a first electrode; a second electrode opposite the first electrode; and one or more organic material layers interposed between the first electrode and the second electrode and including a photoactive layer, wherein one or more of the organic material layers comprise the copolymer of claim
 1. 17. The organic solar cell of claim 16, wherein the organic material layers comprise one or more selected from the group consisting of an electron donor and an electron acceptor, wherein the electron donor is the copolymer.
 18. The organic solar cell of claim 17, wherein the electron acceptor is selected from the group consisting of fullerene, fullerene derivatives, carbon nanotubes, carbon nanotube derivatives, vasocuproin, semiconductor elements, semiconductor compounds, and combinations thereof.
 19. The organic solar cell of claim 17, wherein the electron acceptor is a C60 fullerene derivative or a C70 fullerene derivative.
 20. The organic solar cell of claim 17, wherein the copolymer and the electron acceptor are mixed with each other at a weight ratio of 1:0.5-1:4.
 21. The organic solar cell of claim 19, wherein the polymer and the C60 fullerene derivative or the C70 fullerene derivative are mixed with each other at a weight ratio of 1:0.5-1:4.
 22. A method for fabricating an organic solar cell, the method comprising the steps of: preparing a substrate; forming a first electrode on a region of rear sides of the substrate; forming on the first electrode an organic material layer comprising the copolymer of claim 1; and forming a second electrode on the organic material layer. 